of current literature on the platinum metals and their alloys

PROPERTIES

Anisotropy and Magnetostriction of Pt-Fe Alloys

Temperature and magnetic field dependencies of magnetisation, magnetostriction and thermal expansion were measured for ordered Pt-Fe alloys in the range 25−32at.%Fe of the transition from antiferromagnetism to ferromagnetism, through formation of clusters embedded in the antiferromagnetic matrix. Anisotropy of the critical fields were determined and the reorientation of the vector of antiferromagnetism was followed. Tetragonal distortion of the lattice accompanies the change of the effective anisotropy field.

Solubility of Protium, Deuterium, and Tritium in the α Phase of Palladium

r. lässer, Phys. Rev. B, 1984, 29, (8), 4765–4768

The first solubility determinations of T in bulk Pd are presented for the pressure range 0.016 ≤ p ≤ 1.33 bars, temperature range 60−400°C and concentration range, x, in PdTx of 0.0015−0.02. Also the first comparative study of the pressure-composition-temperature relationship of all H isotopes in Pd at low concentrations is described.

Some Transport Properties of Palladium Films

The effect of deposition rate and substrate temperature on the electrical resistivity, TCR and thermoelectric power of Pd films of 2−25nm thickness was found to be marked. Higher rates of deposition and substrate temperatures result in larger grains and hence changes in transport properties.

Effect of Heat-Treatment on the Hydrogen Sensitivity of ZnO Thin Films Loaded with Palladium Salts

Porous ZnO thin films were impregnated with Pd salts from their aqueous solutions, heat treated and assessed for H2 sensitivity. During impregnation of PdCl2, a ZnCl2.4Zn(OH)2 phase is formed, in a surface region which retards the appearance of the H2 sensitivities. By heating the sample at 140−200°C this phase is decomposed, but the impregnated PdCl2 is not decomposed, and a remarkable H2 sensitivity appears, even at room temperature. Similar situations hold in the loading of other Pd salts.

Cu-Rh single crystal alloys containing 1.5−15 at.% Rh were grown unidirectionally from the melt. A dendritic-cellular or sometimes dendritic structure as predicted by Titler’s criteria occurred, and could be identified by microscopy after chemical etching. It is shown that this microsegregation could be reduced by high temperature annealing. Times required to homogenise the solidification structures are shorter than the values predicted by the Fleming model.

Electrical Resistance in Superconducting Amorphous Alloy Zr70lr30

The electrical resistance of Zr70Ir30 (ρ = 300μ Ω cm, Tc=3.67K) was examined. The resistance increases by 3.7% on cooling from 300K down to 10K where it has a hump, and then decreases rapidly approaching Tc. Above 27K any magnetoresistance is not detected, but between 1.7K ≤ T ≤ 27K a positive magnetoresistance is seen and becomes saturated above Hs = 12−13T.

The chemisorption behaviour of a range of organic and inorganic molecules on the basal plane of Ru, Ru(001) was studied. The close-packed Ru surface proved to be very reactive and most of the studied molecules were irreversibly chemisorbed at 25°C. Only CO, PF3, CF3CN, HCN and (CN)2 showed some degree of molecular thermal desorption after adsorption at 25°C.

CHEMICAL COMPOUNDS

Synthesis of the First Pt-Au Cluster by an Unexpected H+-Substitution at trans -PtH(Cl)L2

A New Type of Decaosmium Cluster Geometry: the Synthesis and X-Ray Structure Analysis of Os10(S)2(CO)23

Pyrolysis of Os3(CO)12 with elemental S gives a range of clusters including Os3(S)2(CO)9, Os5S(CO)15, Os6(CO)18, Os7(S)2(CO)20 and Os10(S)2(CO)23. X-ray analysis shows that the last cluster has a new type of Os10 metal core geometry.

Pentamethylcyclopentadienyl Diruthenium Chemistry

The chemistry of the di-Ru centre, when stabilised by η -C5Me5 ligands, provides examples of new organic transformations such as isomerisation of ethylene to ethylidene and addition of ethylene to vinylidene. It also provides examples of new species such as Ru2(CO)2(μ -H2) (η -C5Me5)2.

The electrochemical reduction of nitrobenzene and nitrobenzene sulphonic acid was studied on Pt-S.P.E. prepared with Nafion as the S.P.E. material. The reduction of m-nitrobenzene sulphonic acid yielded metanilic acid with very high current efficiency. No reaction selectivity was observed between the two products on Pt-S.P.E., although conditions were favourable to p-aminophenol production.

The reactions of methyl viologen ions, MV2+ and MV+ and H2 in the presence of colloidal Pt were investigated by pulse radiolysis. In pH range 1.5–4 all the reducing species were converted into H2. At pH 10, practically all the reducing species produce MV+, while from pH 6–8 the predominant species were Pt particles loaded with H2 as hydride ions.

The formation of thick hydrous oxide films on Pt under triangular potential cycling conditions was studied as a function of sweep rate, sweep limits and pH. The results showed that increasing the cycling rate (from 5−100V/s) decreased the optimum upper limit (from 2.8−2.2V in acid) for thick film growth. Hydrous oxide growth was observed in both acid and base but not at intermediate pH values of 4.0−9.0. A brief study of the methanol electrooxidation reaction at initially smooth Pt activated by potential cycling and followed by cathodic reduction of the hydrous film, showed that excellent control of the surface roughness and, hence, the level of electrocatalytic activity of the electrode surface was possible.

Specific Features of the Adsorption of Organic Compounds on Platinum at High Positive Potentials. Methanol Solutions

Studies were made of the mechanism of adsorption of organic compounds on Pt anodes in aqueous and methanol solutions. The effect of the potentials, time of adsorption, volumetric concentration of adsorbate and potential of electrosorption on the amount of firmly adsorbed particles and the nature of the solvent was studied. Detailed explanations are provided.

Potentials of Zero Charge and the Electric Double Layer Structure of Platinum and Palladium in Dimethylsulphoxide

Curves of the differential capacity were measured on renewable Pt and Pd electrodes in perchlorate solutions and alkali metal halogenides in dimethylsulphoxide (DMSO). The potentials of zero charge were found to be −0.15 and 0V for Pt and Pd, respectively. A considerable surface activity of DMSO on Pt and Pd was established together with the growth of specific adsorbed anions in the order ClO4−<Cl−<Br−<I− and weak surface activity of cations which increased in the order Li+<Na+<K+.

Effect of Platinum Elements Additions on the Active Dissolution of Plastic Chromium in Sulfuric Acid

Alloys based on plastic Cr with 0.1−0.4wt.% Ru, Pt, Ir or Pd were investigated in 40% H2SO4 in the active state under cathodic polarisation (−0.175V). All the studied additions of delaying elements are responsible for the reduced anodic dissolution of Cr. Two mechanisms decelerated the dissolution.

Surface and substrate H potential measurements were used to find rates of permeation of dissolved H2 molecules to and from Pd and Pd alloy electrode surfaces through the Brunner-Nernst layer. These cojoint measurements made it possible to compare the upper limiting H chemical potentials at catalytically active surfaces under H bubble evolution during electrolysis in acid, alkaline and neutral salt solutions. (57 Refs.)

Hydrolysis of the Palladium(II) Ion in a Sodium Chloride Medium

The hydrolysis of the Pd(II) ion in a NaCl medium was studied at 25°C by the e.m.f. method. The extent of the Pd hydrolysis depends upon the concentration of both Pd and the NaCl medium. Thus the extent of hydrolysis increases with increasing Pd concentration at a definite pH, but decreases with increasing NaCl concentration. The stability constants of the complexes obtained, PdOH+ and also differ slightly, depending upon the NaCl concentration.

Dioxygen Evolution from Inorganic Systems. Water Oxidation Mediated by RuO2 and TiO2-RuO2 Colloids

The kinetics of reduction of aqueous solutions of CeIV and in the presence of catalytic amounts of RuO2 colloids stabilised with polybrene and colloidal TiO2 particles loaded with RuO2 have been investigated by stopped-flow spectro-photometric techniques. The effect of pH, catalyst preparation and loading concentration have been considered. The TiO2/RuO2 colloidal particles (45nm radii) are extremely active catalysts.

Studies of the Stability of RuS2 Single Crystals and the Photo-Oxidation of Halides

Anodic photocorrosion of n-RuS2 is very slow under moderate conditions but can be accelerated under extreme conditions of high potentials and rapid O2 evolution. The stability is mainly thermodynamic, but may be kinetic to some extent. RuS2 shows an onset of photocurrent which is shifted strongly to lower potentials in the series Cl−, Br−, I−. This is related to improved kinetics of the oxidation reaction due to adsorption of the intermediate species.

The first use of vesicle-stabilised, in situ formed, Rh catalyst-coated colloidal semiconductor CdS in artificial photosynthesis is reported. Band-gap excitation by visible light (λ > 350nm) of Rh-coated CdS in dihexadecylphosphate surfactant vesicles produced H2 in the presence of thiophenol, and the H2 production was sustained for approximately 48h. After 48h, more than 90% of PhSH was consumed. These systems may provide means for viable solar energy conversion.

Photochemistry of the Tris(2,2′-bipyridine)Ruthenium(II)-Peroxydisulfate System in Aqueous and Mixed Acetonitrile-Water Solutions. Evidence for a Long-Lived Photoexcited Ion Pair

The photooxidation of by peroxydisulphate, was investigated by steady-state luminescence quenching and emission lifetime techniques in aqueous and mixed CH3CN-H2O solutions. The results are consistent with the formation of a ground-state ion pair . The lifetime of the photoexcited ion pair-ion pair association constant and oxidative rate constant are reported for aqueous and CH3CN-H2O solutions. The lifetime of the photoexcited ion pair is unusually long, ranging from 0−11 μ s in H2O to 0−53 μ s in 50% CH3CN.

Photosubstitution Reactions of Ru(bpy)2 XYn+ Complexes

d. v. pinnick and b. durham, Inorg. Chem. 1984, 23, (10), 1440–1445

The quantum yields for the photosubstitution of a series of Ru(bpy)2XYn+ complexes have been measured. The ligands X and Y span the range of the spectrochemical series from Cl− to CO. The correlation between the energy of the lowest energy charge-transfer transition and quantum yield is discussed.

Improvement of the Photoelectrochemical Change of H2S over CdS Suspensions Using RuS2 as a Catalyst

Illumination of a suspension of CdS particles loaded with 0.5wt.% RuS2 leads to photocatalytic H2 evolution from alkaline solutions with a formal quantum efficiency of 0.12 at 47onm; in comparison with the analogous system, CdS/0.5wt.% RuO2, this represents an improvement by a factor of 7.

LABORATORY APPARATUS AND TECHNIQUE

The preparation and evaluation of Pd-PdO pH urea electrodes, based on the combination of immobilising urease are described. Full response of the urea electrode was obtained five minutes after transferring the electrode into the test buffer solution, the response characteristics were sensitive to details in the urease-BSA coating of the Pd-PdO pH electrode, and gave reproducible results. The electrode was stable for more than three weeks when EDTA was added to the test and storage buffer solutions.

Circularly polarised 129keV γ -rays from oriented 191mIr nuclei were used to measure the Compton profile of magnetic electrons in ferromagnetic Fe. Radioactive isotope 191Os (which decays to 191Ir) in Fe metal, 3He/4He dilution refrigeration and a solid state detector with a large active diameter remarkably improved the accuracy of the magnetic Compton profile measurement.

HETEROGENEOUS CATALYSIS

Kinetics of Hydrogenation of Melted Benzoic Acid on Palladium Catalyst

The rate of hydrogenation of melted benzoic acid was measured on suspended Pd/activated C catalyst at 130, 150 and 170°C and H2 pressure of 0.8−5MPa. An agreement was observed between the kinetic equation previously established and the present measurement. The kinetic equation could be applied to hydrogenation processes of benzoic acid.

Hydrogenolysis of Alkanes. Part I. – Hydrogenolysis of Ethane, Propane and n-Butane on 6% Pt/SiO2 (EUROPT-1)

The hydrogenolysis of ethane, propane and n-butane was studied on a 6.3%Pt/SiO2 catalyst (EUROPT-1). Treatment of the catalyst in H2 at 623−1173K led to a loss of capacity for H2 chemisorption greater than that attributable to an increase in particle size and to an even greater loss of activity of n-butane hydrogenolysis, which was partly restorable by oxidation. Extensive reorganisation of the metal occurs during a short oxidation at 873K.

Catalysis of the Exchange of Hydrogen and Carbon Isotopes in the Water/Hydrogen and Bicarbonate/Formate Redox Couples: A Comparison of the Exchange Current Densities on Palladium

The exchange of H and C isotopes in the CO3H−/HCO−2 aqueous redox couple occurs at a rate that is of the same order of magnitude as the H isotope exchange in the H2O/H2 aqueous redox system at 298K, using a Pd based heterogeneous catalyst. The catalysts were Pd, Pt on C, PQ.

A Study of the Structure Sensitivity of the Propylene Hydrogenation Reaction over Supported Platinum and Palladium Catalysts

Propylene hydrogenation was investigated over a series of Pt/SiO2 and Pd/SiO2 catalysts; preparations, pretreatments and morphologies were examined. On Pt/SiO2 prepared by impregnation a four-fold enhancement in the turnover frequency occurred as the temperature of treatment in H2 decreased 450°C to −50°C. Pd/SiO2 had a maxima in the turnover frequency at a H2 treatment temperature of ∼100°C. Formation of β -phase of Pd hydride reduced the catalytic activity. Pd catalysts were much more active than Pt catalysts in hydrogenating propylene.

The Oxidation of CO and Hydrocarbons over Noble Metal Catalysts

y.-f. yu yao, J. Catal., 1984,87, (1), 152–162

The oxidation of CO, C3H6, 1-hexene and toluene under excess O2 was studied over Pt, Pd and Rh in the form of unsupported wires or supported on γ -Al2O3 or CeO2/Al2O3. The kinetics were affected by the state of metal dispersion, pretreatment temperature, reaction conditions and the presence of CeO2. Two types of surface sites are postulated to explain the results.

Effects of Catalyst Addition to Coal on CO2 Adsorption Kinetics of Coal and Char

The surface area of Illinois No. 6 coal, impregnated with a series of C gasified catalysts, including Ru, Pd, Pt and Rh was measured by CO2 adsorption before and after pyrolysis. Catalyst addition decreased the surface area of coal accessible to CO2 in all cases.

Preparation of Catalysts. Part 2. Depositing a Metal Compound on a Support. Impregnation and Drying

Impregnation and drying, which are two of the operating principles involved in preparing supported metal catalysts are examined. An analysis of the different phenomena accompanying the drying of a simple system composed of one or two pores, then of a more complex system made up of a support with a wide pore distribution, is given. Among complexes examined are

The synthesis of aromatic hydrocarbons from CO and H2 was studied under pressure using Pd/SiO2 and zeolites. Combination of Pd/SiO2 with H-ZSM-5 or H-mordenite gave aromatic hydrocarbons with selectivities > 50%. Pd/SiO2 with H-Y gave few aromatics. Tetramethyl and pentamethyl benzenes were mostly formed on H-ZSM-5, significantly different from aromatics formed by the methanol reaction on H-ZSM-5.

Optimize Syngas to Naphtha over Ruthenium Catalysts

The optimisation of a catalyst system for production of crackable feedstock from the partial combustion cracking byproduct syngas was investigated. A series of studies with a number of Co and Ru catalysts using various supports, such as C, Al2O3, H-ZSM-5 zeolite, silica gel and silicalite were performed. Studies were also done with K-promoted Ru/Al2O3 catalysts and Ru-Ni/Al2O3 catalysts. Results were compared, selectivities examined and the effects of surface area were measured. The H2:CO ratio was fixed by the conditions of the ethylene production process, and to maximise the C2+ selectivity to obtain the highest possible yield of feedstock crackers to ethylene. An optimised K-promoted Ru/Al2O3 catalyst had campaigns of over 1000 hours on stream. The C2+ selectivities averaged ∼90%.

Promoting Effect of V, Mo, W and Re on the Rate of C-O Bond Dissociation of Adsorbed CO in Methanation on Ru/Al2O3

Studies of the effect of the addition of V, Mo, W and Re on the rate of C-O bond dissociation of adsorbed CO in methanation on Ru/Al2O3 catalysts was made using pulse surface reaction rate analysis, coupled with an emissionless diffuse reflectance i.r. spectrometer. The addition of these elements was found to increase greatly the rate of dissociation.

High Molecular Weight Hydrocarbons from the Fischer-Tropsch Process with a Pre-oxidized Ruthenium Zeolite Catalyst

The catalytic performance of zeolite based Ru catalyst in the Fischer-Tropsch reaction depends on the sequence of oxidation/reductions to which they are subjected. With finely divided Ru particles, obtained by reducing [Ru(NH3)6]3+-exchanged synthetic faujasitic zeolite, CH4 is the main product, but when the zeolite is first oxidised in air at 400°C, forming RuO2 crystallites which can then be reduced, longer-chain hydrocarbons are produced at low reaction temperatures (155°C).

HOMOGENEOUS CATALYSIS

Gas Phase Acetoxylation of 1,3-Butadiene over Palladium Catalysts. Part 1. The Catalytic Activity and Structure of Pd-Sb-KOAc Catalysts

h. shinohara, Appl. Catal., 1984, 10, (1), 27–42

The gas phase acetoxylation of 1,3-butadiene over Pd catalysts was studied. The Pd-KOAc catalyst gave a very low activity and selectivity to 1,4-diacetoxybutene-2. The main product was 1-acetoxy-1,3-butadiene but, by adding some third components to the catalyst, higher activity and selectivity were obtained; Sb and Bi were the most effective third components. The highest activity was obtained at ∼0.4 Sb:Pd atomic ratio. It is concluded that the active species on the Pd-Sb-KOAc catalyst is an inter-metallic compound, such as Pd3Sb.

Mechanistic and kinetic studies of Pd-catalysed hydrogenation at atmospheric pressure and 30−100°C were carried out with methyl sorbate, methyl linoleate and conjugated linoleate. Homogeneous Pd catalysts and particularly Pd-acetylacetonate [Pd(acac)2] were significantly more selective than Pd/C in the hydrogenation of sorbate to hexenoates, mainly trans-2-hexenoate.

Synthetic Applications of the Palladium-Catalyzed Oxidation of Olefins to Ketones

j. tsuji, Synthesis, 1984, (5), 369–384

A review of the oxidation of olefins to ketones with Pd(II) salts is presented. Emphasis is placed on the catalytic oxidation of terminal olefins to methyl ketones and the application to organic synthesis. Also regioselective oxidation of some internal olefins by the participation of O functions is given. (120 Refs.)

Oxo Complexes of Ruthenium (VI) and (VII) as Organic Oxidants

Oxidation of a variety of saturated and unsaturated primary and secondary alcohols by [RuO4]2−, [RuO4]−, trans-Ba [Ru(OH)2O3], [RuO2Cl3]− and [RuO2(bipy)Cl2] was studied. [RuO4]2− was found to be useful catalytically in conjunction with [S2O8]2− under basic aqueous conditions. Both [RuO4]2− and [RuO4]− oxidise primary alcohols to carboxylic acids and secondary alcohols to ketones. The new species [PPh4][RuO2Cl3] and also [RuO2(bipy)Cl2] cleanly oxidised a wide range of alcohols to aldehydes and ketones without attacking double bonds.

CORROSION PROTECTION

Detection of Hydrogen Generated by Corrosion Reactions Using a Solid Electrolyte Probe

s. b. lyon and d. j. fray, Mater. Perform., 1984, 23, (4), 23–25

A solid state electrolyte probe for H2 detection either inside solid steel pipes or in the environment has been developed. The probe has different designs depending on the application but all use Pd. The probes are used to monitor corrosion in steel.

ELECTRICAL AND ELECTRONIC ENGINEERING

Thermoelectric Effects in Cold Work in Pt/10%Rh and Pt/13%Rh Versus Pt Thermocouples

r. e. bentley and t. l. morgan, Metrologia, 1984, 20, (2), 61–66

The effects of cold work introduced in handling Pt-Rh:Pt thermocouples have been investigated. Changes in the Seebeck coefficient of up to −40nV/°C and errors in calibration of up to −0.4% were found. Above 200°C recovery in the Seebeck coefficient toward its pre-cold-worked value occurred at an increasing rate with temperature, but in the Pt-Rh leg, unlike the Pt leg, the recovery was incomplete. A residual effect, attributed to Pt-Rh, of up to −4μ V remained in the thermocouple e.m.f. after recovery anneals had been applied. Recommendations are made for handling high quality Pt-based thermocouples.

The Effect of Environment and Materials Properties on the Friction and Wear Behaviour of Precious Metal Electrical Contact Alloy Couples

The friction and wear behaviour of Pd base (ASTM B540) alloy couple and Au base (ASTM B541) were tested in air with 35−45% relative humidity, high purity air and in ultra high purity He. The microstructures and hardness were varied by age hardening, heat treatments and/or cold rolling. The poorest friction performance occurred in the He atmosphere. O2 in the environment improved the unlubricated friction performance significantly.

High-Efficiency Ion-Implanted Silicon Solar Cells

The development of solar cells with AM1 conversion efficiency of 18% is reported. The cell comprises an n+-p-p+ structure, fabricated from float zone Si of resistivity 0.3 Ω cm. The front contact pattern made for Ti-Pd-Ag yielded a shadow loss of 3−4%. The back contact was formed by full-area Ti-Pd-Ag metallisation. The growth of SiO2 passivation for reduction of the surface recombination velocity was shown to be important for high cell performance.

Properties of Galvanic Pd-Ni-Coatings at Plug Contact

The properties of PdNiX (X=20,35) electrodeposits (with and without AuCo flash) are discussed in comparison to AuCo and Pd+Au−Co(fl). SEM and optical investigations, and measurements of microhardness, frictional forces, contact resistance and internal stress of the electrodeposits were used to describe the friction wear characteristics. The electrodeposits were corroded in H2S, SO2 and NO2 at 400 ppb each for 6 days, and after exposure at 398K and 473K for 96 hours. The PdNi20 + AuCo(fl) layers on connectors were found to be at least equivalent to high carat AuCo and Pd + AuCo(fl). The Pd and Ni were in solid solution.

Measurement of the Tunnelling and Hopping Parameters in RuO2 Thick Films

Thick film resistors containing a mixture of conductive RuO2 and Pb5B2SiO10 have been produced on [(Al2O3)0.96(MgO)0.04] substrates. The TCR of the films was measured for different particle size and concentration of the conductor particles. The TCR was a function of temperature in all the films. From the measured values of negative TCR the tunnelling parameter α and hopping parameter β were determined. The results suggest that hopping is important for the low concentration films.